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Do I have bad luck or am I missing something?

I have a Panasonic TH-50PZ80U... It came to me giving the 12 binks. It formerly belonged to a co-worker who was getting the same blink code a while ago so he took it to a repair shop. It worked after that for several months, maybe as much as a year, and then it came back. He actually sent it to me for repair before giving it to me, but I was unable to troubleshoot it at that time because the problem went away by itself, but then came back.

I got my hands on the troubleshooting guide for the TV, followed the flowchart and found that the issue was in the power supply: The 15V line was dead.
There are no shorts between the 15V line and ground and the resistance between them is approximately 1.2K ohms.

I ordered a replacement power supply for the TV, put it in and... 12 blinks! :tears:
After some troublshooting I find that again, it's a dead 15V line!!

I am suspicious of two different power supply boards doing the same thing, but I am at a loss for what else to check. There is no short to ground on the 15V line and all the troubleshooting flowcharts point to it being a bad P board.